1. Field of the Invention
The present invention relates to a thermal roller used in a fixing device for fixing a thermally meltable recording material, such as toner, onto a recording sheet, such as a sheet of paper.
2. Description of the Related Art
There has been a fixing device used for fixing toner images onto a recording medium, such as a paper sheet. The fixing device is used in image forming devices such as electrophotographic printers and copiers. The fixing device is provided with a thermal roller. One frequently used thermal roller is formed from a stainless steel or aluminum tube with a halogen lamp disposed in its interior. The halogen lamp generates heat when illuminated. The heat from the halogen lamp heats the entire roller to a fixed temperature.
However, the halogen lamp is merely disposed in the center of the cylindrical tube and is not in intimate contact with the roller surface. Therefore, heat is inefficiently transferred from the halogen lamp to the cylindrical tube so that a great deal of time is required from when the halogen lamp is turned on until the thermal roller is heated up to a predetermined temperature required for fixing toner onto a recording sheet.
Japanese Patent-Application Publication (Kokai) Nos. HEI-9-138605 and HEI-9-179423 each disclose a thermal roller formed with a resistance-type heat-generating layer at its inner peripheral surface. The resistance-type heat-generating layer serves as a heat source for the thermal roller. As shown in FIGS. 1(a) to 1(d), the thermal roller is formed from a metal pipe 101; a resistance-type heat generating layer 102 including a heat-resistance insulation layer and a thermal heat-generating body disposed on the inner peripheral surface of the metal pipe 103; and a pressing body 103a or 103b mounted to the inner surface of the heat-resistant insulation layer 102. The heat-resistant insulation layer 102 is formed from a film member of polyimide, for example, and a thermal body fixed to the surface of the film member. The pressing body is formed from foam rubber or a hard foam resin material. Japanese Patent-Application Publication (Kokai) No. HEI-9-179423 describes the pressing body 103a, which as shown in FIGS. 1(a) and 1(b), has a solid columnar shape. Japanese Patent-Application Publication (Kokai) No. HEI-9-138605 describes the pressing body 103b, which as shown in FIGS. 1(c) and 1(d), has a hollow cylindrical shape.
Pressure within the foam rubber or the foam resin material of the pressing body 103a, 103b presses the heat-resistant insulation layer 102 against the metal pipe 101 to fix the heat-resistant insulation layer 102 against the metal pipe 101. The thermal body is pressed directly by the pressing body 103a, 103b into intimate contact with the inner peripheral surface of the metal pipe 101. With this configuration, heat from the thermal body is properly transmitted to the metal pipe 101.
Japanese Patent-Application Publication (Kokai) No. HEI-8-194401 discloses a thermal roller 110 shown in FIGS. 2 and 3. The thermal roller 110 includes a roller body 111 formed in a hollow cylindrical shape from a material having good thermal conductivity; a clinging prevention layer 112 formed on the outer peripheral surface of the roller body 111, and a resistance-type heating member 113 attached to the inner peripheral surface of the roller body 111.
The resistance-type heating member 113 includes an insulation film member 114 and a resistance-type heating body 117. The insulation film member 114 is formed from a polyimide resin film having heat resistance and electrical insulation properties. The resistance-type heating body 117 is a flexible heat-generating sheet attached onto the surface of the insulation film is member 114 and is configured from a resistance member 117a and electrodes 117b. The resistance member 117a is formed from a single or a plurality of stainless steel or copper foil films etched to a predetermined pattern on the insulation film member 114. The electrode 117b is provided for supplying power to both terminals of the resistance member 117a. The cross-sectional area of the resistance member 117a changes in the axial direction of the roller body 111 in order to adjust the temperature at the outer peripheral surface of the roller body 111 to a uniform temperature.
The thermal roller disclosed in Japanese Patent-Application Publication (Kokai) No. HEI-8-194401 is assembled by first coating a heat-resistant adhesive, which has no adhesive properties at room temperature, to the inner surface of the insulation film member 114. The insulation film member 114 is then inserted into the roller body 111. Next, the resistance-type heating member 113 is brought into contact with the inner peripheral surface of the roller body 111 using air pressure and the like. Then, the resistance-type heating member 113 and the roller body 111 are heated and fixedly adhered to each other in a high temperature oven.
Because the resistance-type heating member 113 is configured from a heat-generating sheet formed by prefixing the resistance-type heating body 117 onto the insulation film member 114. when the thermal roller 110 is assembled, operations for fixing the resistance-type heating member 113 to the roller body 111 can be easily performed. However, it would be desirable if the number of steps in the assembly process could be decreased or the steps further simplified somehow.